Hydrocracking process with tri-metallic catalyst

ABSTRACT

The instant invention relates to a novel hydrocracking process wherein carbon-carbon bonds are ruptured and carbon-hydrogen bonds are formed in the presence of hydrogen and a catalyst comprising platinum, iridium and rhodium supported on an inorganic refractory oxide. This process relates to the dealkylation of alkyl aromatics to form lower molecular weight aromatics, for example, alkylbenzenes such as ethylbenzene, xylene, toluene, etc. may be converted to benzene in the process of the instant invention. The process can also be used to convert a gas-oil fraction to gasoline by converting the higher molecular weight constituents of the gas-oil fraction to lower molecular weight products.

United States Patent Sinfelt et al.

HYDROCRACKING PROCESS WITH TRl-METALLIC CATALYST lnventors: John H.Sinfelt, Berkeley Heights;

Allan E. Barnett; James L. Carter, both of Westfield, all of NJ.

Exxon Research & Engineering Co., Linden, NJ,

Filed: Jan. 30, 1975 Appl. N0.: 545,371

Related US. Application Data Continuation-impart of Ser. No. 380,833,July 19, 1973, Pat. No. 3,871,996.

Assignee:

US. Cl 208/111; 208/112; 252/455 R; 252/460; 252/463; 252/472; 260/672 RInt. Cl. C10G 13/06; CO7C 3/58 Field of Search 208/111, 112; 260/672 R;252/460, 463, 472

References Cited UNlTED STATES PATENTS 2/1916 Mittasch 252/466 PT 2/1954Strecker 4/1954 Rosenblatt... 252/466 PT Primary ExaminerDelbert E.Gantz Assistant ExaminerG. E. Schmitkons Attorney, Agent, or FirmRobertJ. Baran [57] ABSTRACT The instant invention relates to a novelhydrocracking process wherein carbon-carbon bonds are ruptured andcarbon-hydrogen bonds are formed in the presence of hydrogen and acatalyst comprising platinum, iridium and rhodium supported on aninorganic refractory oxide. This process relates to the dealkylation ofalkyl aromatics to form lower molecular weight aromatics, for example,alkylbenzenes such as ethylbenzene, xylene, toluene, etc. may beconverted to benzene in the process of the instant invention. Theprocess can also be used to convert a gas-oil fraction to gasoline byconverting the higher molecular weight constituents of the gas-oilfraction to lower molecular weight products.

12 Claims, No Drawings HYDROCRACKING PROCESS WITH TRI-METALLIC CATALYSTH. Sinfelt, A. E. Barnett, and]. L. Carter, now US. Pat. No. 3,871,996issued Mar. 18, 1975.

FIELD OF THE INVENTlON The instant invention relates to a novelhydrocracking process wherein carbon-carbon bonds are ruptured andcarbon-hydrogen bonds are formed in the presence of hydrogen and acatalyst comprising platinum, iridium and rhodium supported on aninorganic refractory oxide. This process relates to the dealkylation ofalkyl aromatics to form lower molecular weight aromatics, for example,alkylbenzenes such" as ethylbenzene, xylene, toluene, etc. may beconverted to benzene in the process of the instant invention.The processcan also be used to convert a gas-oil fraction to gasoline by convertingthe higher molecular weight constituents of the gas-oil fraction tolower molecular weight products.

BACKGROUND OF THE PRIOR ART Hydro processes are catalytic processescarried out in the presence of hydrogen, wherein hydrocarbon feedstreams undergo hydrocracking, hydrogenolysis, hydrogenation,hydroisomerization and hydrodealkylation reactions. In these processesthe main reactions which take place are the cracking of hydrocarbons,that is, carbon-carbon bonds are ruptured with a net formation ofcarbon-hydrogen bonds. These processes also include removal of sulfurand nitrogen impurities as H 8 and NH Other reactions which take placein the hydrocarbon feed streams during hydro processing includeisomerization of paraffinic hydrocarbons and removal of alkyl groupsfrom alkyl aromatic hydrocarbons. Some specific examples of deak-ylationreactions include dealkylation of alkylbenzenes and alkylnaphthalenes toform lower molecular weight aromatics. For example, methyl andethylnaphthalene can be converted to naphthalene and ethylbenzene andxylene may be converted to benzene and toluene. Thus, it is evident thatthe dealkylation of alkyl aromatics is a specie of the generalhydrocracking processes known in the art.

In hydro processes the presence of hydrogen is necessary to yieldsaturated products and suppress formation of deactivating carbonaceousresidues as well as to allow removal of sulfur and nitrogen impuritiesas H 5 and NH Materials which may be hydro processed include petroleum,coal, shale oil and tar. The process of the instant invention isconcerned mainly with hydro processes wherein there is no net removal ofhydrogen, that is, the process of the instant invention does not includecatalytic reforming.

The instant invention is mainly concerned with the hydrocracking ofhydrocarbon feed streams. Catalysts which are useful in hydrocrackingprocesses are bifunctional catalysts that contain sites for bothcrackingand hydrogenation. The two sites are preferably in close proximity .tominimize fouling of the-catalyst by deposition of sulfur, nitrogen andcoke.

The hydrogenation activity is usually supplied'by a metal which isdeposited .on a support which will have acidic sites to provide thecracking activity. Supports which'may be used include acidic refractoryoxides such as alumina, silica alumina, etc. Silica aluminas includezeolite supports, i.e., crystalline alumino silicates. In thesebifunctional catalysts, a principal role of themetal hydrogenation siteis to keep the acid sites clean and effective by hydrogenating the cokeprecursors which block the acid sites. The metal must be highlydispersed to support this hydrogenation activity.

' The prior art hydrocracking catalysts include cobaltmolybdatecatalysts, and tungsten sulfide on clay. These catalysts have beensubstantially replaced by the palladium on zeolite catalyst which hashigher activity. This catalyst can be operated at a lower temperaturethereby reducing the deactivation rate. This catalyst also has a higheractivity maintenance in the presence of nitrogen and sulfur compounds inthe feed.

The supported platinum-iridium-rhodium catalyst of the instantinvention, which is further described below, shows an even lower rate ofdeactivation by coke, as well as at least similar activity maintenancein the presence of nitrogen and sulfur impurities. It is found that thistrimetallic combination of active metals provides an effectivehydrogenation site, in a manner similar to palladium, but, unlikepalladium, contributes a great degree of hydrocracking activity. Thus,this very active trimetallic combination may be supported on materialsthat are less acidic than zeolites, such as alumina, and still functionas an effective hydrocracking catalyst.

Prior art hydro processes for the dealkylation of aromatics to formbenzene and naphthalene from their alkylated precursors employ catalystsuch as chromiaalumina, cobalt-molybdenum-alumina, nickel-alumina,silica-alumina, nickel-chromia-alumina andcobaltchromium-molybdenum-alumina. These catalysts have been replaced insome of the more recent processes by noble metal catalysts which havehigher activity and activity maintenance and also provide improvedselectivity to the desired aromatic product. In the dealkylation ofalkylbenzenes and alkylnaphthalenes the trimetallic catalysts of theinstant invention show improved activity and activity maintenance overthe prior art noble metal catalysts SUMMARY OF THE INSTANT INVENTION Theinstant invention relates to a process for the hydrocracking ofpetroleum feed streams. In this process, the petroleum feed stream iscontacted with a catalyst comprising platinum, iridium and rhodiumsupported on an inorganic refractory oxide in the presence of hydrogento yield a petroleum fraction characterized as having a lower averagemolecular weight than the starting feed stream. In this process,carboncarbon bonds are ruptured and there is a net formation ofcarbon-hydrogen bonds.

The petroleum feed stream may range from heavy naphtha to a deasphaltedresiduum and may contain sulfur and nitrogen impurities. in a preferredembodiment of the instant invention, an alkylbenzene or analkylnaphthalene-containing feed stream is contacted with theplatinum-iridium-rhodium catalyst of the instant invention underconditions whereby the alkyl aromatics are converted to benzene andnaphthalene respectively in the presence of hydrogen.

The catalyst compositions used in the process of the present inventioncomprise platinum, iridium and rhodium in a highly dispersedrnetallicstate on a refractory support. The catalysts will comprise at least 0.05wt.

rhodium, at least 0.1 wt. platinum, and'at lea'st 0.1 wt. iridium basedon total catalyst weight. Preferably, the catalyst compositions of theinstant invention will comprise from 0.1 to 1.0 wt platinum, from 0.1 to1.0 wt. iridium, and from 0.05- to 0.5 wt.v% rhodium. The total metalsurface area 'of the catalyst pref,- erably is at least 200 squaremeters'per gram of said total metaL'as-determined bythe gaschemisorption method described by Sinfelt and Yates, J. Catalysis, 8,82-90 (1967). The catalyst support is preferably substantially free ofalkali or alkaline earth metal compounds and, as further describedbelow, will give most effective performance when prepared in a manneravoiding exposure'of the catalyst to air or oxygen at temperatures aboveabout 425C. When'the catalysts are prepared in this manner, highlydispersed multimetallic clusters are formed, which are preferred to thecompositions prepared by the general. techniques known in the art forpreparing reforming catalysts, i.e., calcination in air at temperaturesof 500C. or higher.

The catalyst of theinstant invention is preferably prepared bycoimpregnation of the supports using a solution of the catalyst metalprecursors. However, in the case where a zeolite is used as the supportmaterial ion exchange of the metals into the zeolite is an alternatepreferred method of depositing the metals onto the support. [on exchangeof metals into zeolites is well known in the art. coimpregnation or inthe case of zeolite supports ion exchange using a single solutioncomprising the precursors for all three metals dissolved therein isgenerally favored over sequential techniques to enhance the formation oftrimetallic clusters. It should especially be noted that such clusterformation is desirable in preparing the instant trimetallic catalysts.Thus, the preparation of the catalystsof the instant invention comprisescontacting a solution of soluble metallic precursors with the support atsuitable impregnating or ion exchange conditions. The catalyst metalprecursor-solution is preferably aqueous and precursor compounds maybeselected from the group consisting of chloroplatinic acid,chloroiridic acid, rhodium trichloride, iridium trib romide, ammoniumchloroiridate, ammonium chloroplatinate, platinum amine salts,rhodiumnitrate, etc. In general, anyprecursor salt which is watersoluble may be used. The impregnated or ion exchanged catalyst is thendried. During drying, it is important that the catalyst not be contactedwithoxygen if the temperature of drying exceeds about 425C. The catalystmay be driedby contacting with an inert gas or by applying a vacuum tosaid impregnated or io'n exchanged catalyst. The catalyst, whensufficiently dried, is contacted with a reducing atmosphere to reducethe metallic precursors to the desired metallic form. Preferably,'thecatalyst is reduced in hydrogen. The catalyst is then a dispersedp'olymetallic cluster. The metallic atoms which constitute the clusterwill Refractory inorganic oxide materials such as alumina, silica'alumin'a, and alumino silicates are the preferred catalyst supportmaterials. In general, superior results 'are ,obtained when acidicsupports are employed. Aluminasandsi lica-aluminas, including zeolites,are the preferred support materials. The support materials mentionedabove are'known articles of commerce 'andcan beprepared'for use ascatalyst constituents by many varied techniques. Typically, the supportmaterials are used in the form of spheres, granules, powders, extrudatesor pellets, etc. Theprecise size or shape of the'support material usedisdependent upon many engineering factors not within the purview of theinstant invention. 1

The platinum, iridium, and rhodium exist as components of a polymetallicclusteron the surface of the refractory support. Improved catalystperformance is l obtained 'when'the catalyst is prepared inv the manner[described above, which favors formation of dispersed multimetallic'clusters rather than separate crystallites of the individual metalsz Asdisclosed hereinabove, at

least'0.05 wt'. rhodium, 0.1 wt. platinum, and 0.1 wt. iridium must bepresent. Total metal-concentra- 'tion of the catalyst should be from0.25 to 2.5 wt; As

is known to those familiar with the hydroprocessing of petroleum feedstreams the metals utilizedinthe instant catalyst are costly, and thusminimum amounts must be utilized as long as said minimum amount does beseparated by distances of about 2.5 to 4 Angstroms,

and the average distance between the polymetallic cluster centers is atleast 10 times the average distance between the atoms within a cluster.

The support or carrier component of the catalysts of .the presentinvention is preferably a porous, adsorptive material having a surfacearea, as determined by the Brunauer-Emmett-Teller (BET) metho'chofabout20 to 800, preferably 100 to 300, square meters/gram, The supportmaterial should be substantiallyrefractory at the temperature andpressure conditionsutilized in any given hydrocarbon conversion process.

As is taught in U.S. Ser. No. 194,461, filed in the names of J. H.Sinfelt and A. E. Barnett, on November 1, 1971, herein incorporated byreference, iridiumcontaining catalysts mustbe treated carefully toobtain maximum surface area. Thus, itis critical to the instantinvention that prior to reduction to the metal the iridium does notexist in the form of large crystallites of iridium oxide, since iridiumcrystallites of low surface area will be obtained on reduction of saidlarge'crystallites. Agglomerated iridium, however, can be redispersed'by contacting with halogen-containing gases, e.g., chlorine, in asubstantial absence of oxygen as disclosed in-'U.S. Ser. No. 343,304,filed on Mar. 21, 1973, in the name of D. J .C. Yates, and hereinincorporated by-tefere'nce. The'techniques which are-disclosed in U.S.'Ser. No. 343,304 may be conveniently used with the catalyst of theinstant-invention.

The catalyst used in the process of the instant invention is effectivein the presence 'of feedsulfur levels of from 0.1 to 3 percent byweight, i .e., those levels which may be encountered in hydrocrackingheavier-petroleum fractions. However, the performance. of the catalystsystem of the present invention may be affected by the presence ofsulfur or sulfur-containing materials arising from the feed stock orother sources, as when used in the'dealkylation of alkyl aromatics.Accordingly when the catalyst is employed for dealkylation of alkylaromatics, the sulfur content of the catalyst is preferably maintainedat a level less than about: two

atoms of sulfur, preferably less than one atom of sulfur, perfatom ofiridium and additional catalyst metals. The desired low-"catalyst sulfurlevels-are advantageously maintained during the predominant portion ofany dealkylation cycle. Higher catalyst sulfurlevels may beencountered'd'uring some portions-of a run in which case thesulfur'maybe at least partially removed from '5 the catalyst by contacting thesame with sulfurfree feed stock. Finally, the catalyst 'should besubstantially free of alkali metal (Group vlA-);or alkaline earth metal(Group llA') constituents; (less' t han 0.1: wt: since the presence ofbasic components on the catalyst serves to inhibithydrocrackingactivity. w .1

Following the impregnation of the support with the catalyst metalprecusors, the catalystmay be dried at a temperature varying from about100 to 125C. The catalyst may simply be dried in air at the above-statedtemperatures or may be dried by treating the catalyst in a flowingstream of inert gas or hydrogen. The drying step may be followed by anadditional calcination step at a temperature of about 260to 370C. Caremust be taken to avoid contacting the catalyst at temperatures in excessof about 370 to 425C. with air .or other gas of high oxygenconcentration. Otherwise the iridium will be oxidized, with loss ofsurface area, to crystallites of iridium oxide, and the polymetalliccluster structure will not be obtained on reduction.

Additional materials may be present in the catalyst to promote thedesired reactions. For example, ifalumina is the support, halogens suchas chlorine or fluorine may be incorporated in the catalyst to enhancethe acidity. The halogen may be incorporated during the catalystpreparation using, for example, HCl or HP. Alternatively, it may beincorporated after the catalyst is charged to a reactor in a manneranalogous to the chlorine treating of reforming catalysts.

The catalyst compositions of the present invention have uses inprocesses other than hydrocracking. For example, the catalysts can beemployed in the formation of aromatic compounds by contacting thecatalyst with suitable paraffins or naphthenes at a temperature varyi ngbetween about 370 and 540C. and a pressure of less than aboutatmospheres in the presence of hydrogen. The catalysts of this inventioncan also be employed to promote the isomerization of ethylbenzene toxylenes by contacting ethylbenzene with the catalyst at a temperaturevarying from about 200 to 600C. at elevated pressures in the presence ofhydrogen. The catalysts are also useful for promoting hydrogenation,oxidation, polymerization, condensation and other reactions known to theart.

In a typical hydrocracking process, a petroleum feed stream whichcontains various high molecular weight hydrocarbons known in the art toundergo hydrocracking reactions, such as alkyl aromatics, is contactedwith the above-described catalysts in the presence of hydrogen. Thepetroleum feed stream typically contains components boiling in the rangeof 100 to 600C. and as will be known by those skilled in the art, may beany cut from a deasphalted residua to a heavy naphtha. The temperatureof contacting is typically from 200 to 600C., more preferably from 300to 500C. The pressure of contacting is typically from 100 to 10,000 psi,more preferably from 200 to 3,000 psi. The petroleum feed stream ispassed over the catalyst at space velocities varying from about 0.2 to5.0 parts by weight of feed stream per hour per part by weight ofcatalyst (W/Hr/W The mole ratio of hydrogen to hydrocarbon maintainedwithin the reaction zone is between about 1 and 20.

The catalyst is typically used as a fixed bed in a single reactor or ina series of reactors. Alternatively, the catalyst could be employed in afluidized bed or ebulliating bed reactor or in a slurry reactor,depending on the particular application.

The hydrocracking process generally involves the ruptureof carbon-carbonbonds and the net formation of carbon-hydrogenbonds, with a resultingdecease in the average molecular weight of the petroleum feed stream.Thus, typically, alkyl aromatics are converted to lower molecular weightaromatics. For example, alkylnaphthalenes and alkylbenzenes areconverted to naphthalene-and benzene respectively. Thus, the process isuseful for converting low value feed streams into higher value aromaticfractions. 1

An outstanding feature of the instant platinum-iridium-rhodium catalystis its ability to maintain its catalytic activity at commerciallydesirable levels for protracted periods of time. In a typical commercialhydrocracking process, the reaction temperature is increased during thecourse of the run to maintain conversion at a given leveL Raisin g thereaction temperature is necessary because thecatalyst is continuouslydeactivated as coke is deposited on the surface. Unfortunately, thereaction temperature cannot be raised much beyond about 525C. beforerapid catalyst deactivation commences. Therefore, as the reactiontemperature approaches about 525C., it is necessary to regenerate orreplace the catalyst. Typically, a regeneration operation consists ofburning the coke deposits from the catalyst and may also includetreating the catalyst with a gas containing chlorine, HCl, organicchlorides or mixtures thereof to incorporate halogen in the catalyst.

It is desirable to increase the duration of the periods between processstart-up and catalyst regeneration and/or between catalyst regenerationssince valuable production time is lost when the catalyst is beingregenerated. As noted above, the present platinum-iridiumrhodiumcatalyst needs to be regenerated very infre quently.

EXAMPLE 1 A feed stream of vacuum gas oil with a boiling range of 300 to490C, A.P.l. Gr. 21.7, aniline point of 69C., 0.6 wt. sulfur and 2,400wt ppm nitrogen is passed over a catalyst consisting of 0.3% Pt, 0.15%Rh, 0.15% Ir and 0.6% Cl on alumina. The pressure is 2,500 psig, the Hrate is 8,000 SCF/BBl of feed, the temperature is 425C and the spacevelocity is adjusted to obtain the desired conversion level. The producthas a much lower average molecular weight and 50 vol. of the productboils in the gasoline range.

EXAMPLE 2 Meta xylene and hydrogen are passed over a catalyst consistingof 0.3% Pt, 0.15% lr, 0.15% Rh, and 0.6-1.5% Cl on alumina at a pressureof 150-250 psig and at temperatures of 500550C. The mole ratio ofhydrogen to meta xylene is 3-5. The extent of conversion of m-xylene tobenzene and toluene is 50-75 percent, depending on the liquid hourlyspace velocity and the length of time on stream.

What is claimed is:

l. A process for hydrocracking a petroleum feed stream which comprisescontacting said feed stream with a catalyst comprising platinum, iridiumand rhodium supported on an inorganic refractory oxide in the presenceof hydrogen at reaction conditions whereby a petroleum fractioncharacterized as having a lower average molecular weight than thestarting feed stream is obtained.

2. The process of claim 1 wherein said petroleum feed stream has aboiling point of from about to 7 about 600C.

3. The process of claim 1 wherein 'said support is selected from thegroup consisting of alumina, silicaaluminas and aluminosilicates. I

4. The process of claim 3 wherein said support is selected from thegroup consisting of alumina and silica aluminas.

5. The process of claim 4 wherein said catalyst comprises from 0.1 to1.0 wt. platinum, from 0.1 to 1.0 wt. iridium, and from 0.05 to 0.5 wt.rhodium.

6. The process of claim 5 wherein said reaction conditions comprisecontacting said petroleum feed stream with said catalyst at atemperature of from 200 to 600C and a pressure of from 100 to 10,000psi.

7. The process of claim 6 wherein said petroleum feed stream is passedover the catalyst at a space velocity varying from about 0.2 to 5.0parts by weight of feed stream per hour per part by weight of catalyst.

1 8. The process of claim 7 wherein the mole ratio of hydrogen tohydrocarbon maintained within the reaction zone is between about 1 and20.

9. The process of claim 2 wherein said petroleum feed stream comprisesan alkyl aromatic and said reaction product comprises a lower molecularweight aromatic.

10. The process of claim 9 wherein said alkyl aromatic is an alkylnaphthalene, which is converted into naphthalene.

11. The process of claim 9 wherein said alkyl aromatic is an alkylbenzene which is converted to a mixture of lower molecular weight alkylaromatics and benzene.

12. The process of claim 9 wherein said alkyl aromatic is an alkylbenzene which is converted into benzene.

1. A PROCESS FOR HYDROCRACKING A PETROLEUM FEED STREAM WHICH COMPRISESCONTACTING SAID FEED STREAM WITH A CATALYST COMPRISING PLATINUM, IRIDIUMAND RHODIUM SUPPORTED ON AN INORGANIC REFRACTORY OXIDE IN THE PRESENCEOF HYDROGEN AT REACTION CONDITIONS WHEREBY A PETROLEUM FRACTIONCHARACTERIZED AS HAVING A LOWER AVERAGE MOLECULAR WEIGHT THAN THESTARTING FEED STREAM IS OBTAINED.
 2. The process of claim 1 wherein saidpetroleum feed stream has a boiling point of from about 100* to about600*C.
 3. The process of claim 1 wherein said support is selected fromthe group consisting of alumina, silica-aluminas and aluminosilicates.4. The process of claim 3 wherein said support is selected from thegroup consisting of alumina and silica aluminas.
 5. The process of claim4 wherein said catalyst comprises from 0.1 to 1.0 wt. % platinum, from0.1 to 1.0 wt. % iridium, and from 0.05 to 0.5 wt. % rhodium.
 6. Theprocess of claim 5 wherein said reaction conditions comprise contactingsaid petroleum feed stream with said catalyst at a temperature of from200* to 600*C and a pressure of from 100 to 10,000 psi.
 7. The processof claim 6 wherein said petroleum feed stream is passed over thecatalyst at a space velocity varying from about 0.2 to 5.0 parts byweiGht of feed stream per hour per part by weight of catalyst.
 8. Theprocess of claim 7 wherein the mole ratio of hydrogen to hydrocarbonmaintained within the reaction zone is between about 1 and
 20. 9. Theprocess of claim 2 wherein said petroleum feed stream comprises an alkylaromatic and said reaction product comprises a lower molecular weightaromatic.
 10. The process of claim 9 wherein said alkyl aromatic is analkyl naphthalene, which is converted into naphthalene.
 11. The processof claim 9 wherein said alkyl aromatic is an alkyl benzene which isconverted to a mixture of lower molecular weight alkyl aromatics andbenzene.
 12. The process of claim 9 wherein said alkyl aromatic is analkyl benzene which is converted into benzene.